Estimating Time

Being able to estimate the amount of time required for the tasks and activities of a project is a key skill for any project manager. Indeed, in smaller projects that do not have an explicit budget, keeping on schedule is likely to be one of the measures of your effectiveness as project manager.

Getting schedules right

In most cases, estimating task times with any degree of accuracy requires a combination of experience and common sense. However, this presupposes that you have correctly identified the task. When projects are late, it is often because activities have not been thought through or recorded properly, so what seemed like a very straightforward task (such as getting a decision from the finance department, for example) gets estimated as a single event rather than a number of small but significant and connected steps, each taking time and effort.

Estimate the time required

Involving the team

In most small projects, and certainly in an environment where there are numerous projects running side by side, the challenge is not so much to estimate how much effort tasks will take, but how much time someone needs to be able to complete a task alongside the many other demands made of him/her. Involve team members who will be performing critical tasks in your decision-making process. Ask each person for their estimate of the amount of time they will need to be able to complete a certain task, given their other commitments. Be prepared to challenge these estimates if you disagree, but beware of putting undue pressure on people to reduce them.

Using time estimation formulae

Different organizations, industries, and sectors employ different models or formulae to estimate time. At first glance they always seem mathematical, but in most cases their effectiveness is psychological—either overcoming aversion to estimating, or encouraging more careful thought in those who tend to rush in.

Perhaps the most widely known is the PERT formula (Project Evaluation and Review Technique). To use PERT you need three estimates of the time it could take to complete a task or activity:

Use the following formula to estimate the most probable duration for that activity (Te):

The formula can be weighted toward pessimism—if the consequences of a late completion of a particular task are severe, for example—by reducing the Tm multiplier and adding a Tp multiplier:

• The most likely time required (Tm)

• The most optimistic time assessment (To)

• The most pessimistic time assessment (Tp)